JP6467650B2 - Spherical boron nitride fine particles and production method thereof - Google Patents

Description

  The present invention relates to spherical boron nitride fine particles suitable for high thermal conductive fillers and the like and a method for producing the same.

Hexagonal boron nitride (hereinafter referred to as “boron nitride”) has lubricity, high thermal conductivity, insulation, etc., for solid lubricants, mold release agents such as molten gas and aluminum, and heat dissipation materials Widely used for fillers.
Particularly in recent years, the importance of heat dissipation measures has increased due to the high performance of computers and electronic devices, and the high thermal conductivity of boron nitride has attracted attention.

In recent years, addition of boron nitride has been studied for the purpose of imparting high thermal conductivity and insulating properties to resin layers such as resin substrates for printed wiring boards and flexible copper-clad laminates.
The average particle diameter of general boron nitride is several μm to 20 μm, but the thickness of resin layers such as resin substrates for printed wiring boards and flexible copper-clad laminates is about several tens of μm. If the average particle size of the resin is large, the dispersibility in the resin is poor and the surface smoothness cannot be obtained. Submicron class (0.1 μm) boron nitride fine particles are required.

  In order for boron nitride to exhibit high thermal conductivity, it needs to be highly pure and highly crystalline. This does not change even with submicron class (0.1 μm) boron nitride fine particles.

On the other hand, boron nitride has a characteristic scaly shape, and its thermal characteristics are overwhelmingly superior in the major axis or minor axis direction compared to the thickness direction. Therefore, for example, the thermal characteristics of a composite material in which boron nitride is filled in a resin such as silicone are greatly influenced by the directionality of the boron nitride fine particles in the composite material.
However, for example, when a sheet-shaped composite material is produced, in many cases, the boron nitride fine particles lie down in the horizontal direction and do not exhibit sufficient thermal characteristics required in the vertical direction.

  In other words, in order for boron nitride to be suitable as a highly thermally conductive filler, it is necessary to reduce the influence of directionality by making it spherical or agglomerated.

Boron nitride is generally obtained by reacting a boron source (boric acid, borax, etc.) and a nitrogen source (urea, melamine, ammonia, etc.) at a high temperature, and scaly primary particles are formed from boric acid and melamine. Aggregated “pine cone” boron nitride has been proposed (Patent Document 1).
However, the aggregated particle diameter of boron nitride produced by this method is 50 μm or more, and it is difficult to produce submicron-class boron nitride fine particles that are the object of the present invention.

On the other hand, a method for obtaining boron nitride fine particles by a gas phase synthesis method has been reported (Patent Documents 2 to 4).
However, since the boron nitride fine particles obtained by these methods have low crystallinity, the lubricity and high thermal conductivity that are characteristic of boron nitride are insufficient.

JP 09-202663 A JP 2000-327312 A JP 2004-182572 A JP 2010-180066 A

  An object of the present invention is to provide submicron spherical boron nitride fine particles having high sphericity.

The present invention employs the following means in order to solve the above problems.
(1) Spherical boron nitride fine particles having an average particle diameter of 0.01 to 1.0 μm, an orientation index of 1 to 15, a boron nitride purity of 98.0% by mass or more, and an average circularity of 0.80 or more.
(2) Ammonia / boric acid alkoxide boric acid alkoxide having a molar ratio of 1 to 10 and ammonia are reacted in an inert gas stream at 750 ° C. or more within 30 seconds, then ammonia gas or ammonia gas and inert Production of spherical boron nitride fine particles characterized by heat treatment at 1,000 to 1,600 ° C. for 1 hour or more in an atmosphere of a gas mixture and further firing at 1,800 to 2,200 ° C. for 0.5 hours or more in an inert gas atmosphere Is the method.

  According to the present invention, submicron spherical boron nitride fine particles having a high sphericity can be provided.

It is the schematic of the manufacturing apparatus of the boron nitride fine particle of the baking conditions 1. FIG.

It is the schematic of the manufacturing apparatus of the boron nitride fine particle of the baking conditions 2. FIG.

It is an electron micrograph of the spherical boron nitride fine particle of the Example of this invention.

It is an electron micrograph of boron nitride fine particles of a comparative example of the present invention.

In the present invention, first, a white powder is continuously synthesized by a so-called gas phase reaction between volatilized boric acid alkoxide and ammonia in an inert gas stream using a tubular furnace 3 (firing condition 1). Next, this white powder is fired in a tubular furnace 3 (resistance heating furnace) (firing condition 2). Finally, the fired product is placed in a boron nitride crucible and fired in an induction heating furnace to produce boron nitride fine particles (firing condition 3).
In the present invention, “%” is based on a mass standard unless otherwise specified.

  In the present invention, as described above, there are three firing conditions, and the firing conditions are in order of increasing temperature: firing condition 1: 750 ° C. or higher, firing condition 2: 1,000 to 1,600 ° C., and firing condition 3: 1,800 to 2,200. With respect to firing conditions 1 and 2, a resistance heating method can be used as the tubular furnace 3, and an induction heating type electric furnace can be used as the tubular furnace 3 as the firing condition 3. Of course, there is no problem even if an induction heating type electric furnace is used in firing conditions 1 and 2.

  Hereinafter, the present invention will be described with reference to the drawings.

  The apparatus for producing boron nitride fine particles used in firing condition 1 includes a tubular furnace 3 (resistance heating furnace), a reaction tube (quartz tube) 2, a borate alkoxide container 1, a borate alkoxide introduction tube 4, and introduction of ammonia gas. It consists of a tube 5 and a sample collection container 6.

  The spherical boron nitride fine particles of the present invention are continuously synthesized by a so-called gas phase reaction between volatilized boric alkoxide and ammonia. For this reason, an apparatus capable of continuous synthesis is required, and in firing condition 1, for example, an apparatus using a tubular furnace 3 illustrated in FIG. 1 is preferably used.

  The tubular furnace 3 is not particularly limited, but it is preferable to use an electric furnace that is easy to handle.

The basic principle of an electric furnace is to heat a heating element or the like constituting the furnace by energization to heat the inside of the furnace, and the electric furnace is subdivided according to the heating method and the material of the heating element.
In general, heating up to around 1,700 ° C. is possible by a resistance heating method using a heating element, but heating around 2,000 ° C. requires an induction heating method using a coil.
In addition, although silicon carbide, carbon, etc. are used for the material of a heat generating body, it is not specifically limited.

  The material of the reaction tube 2 used in the present invention is not particularly limited, but it is preferable to use alumina or quartz that is chemically stable and has good heat resistance.

  Hereinafter, an outline of firing condition 1 using a quartz tube as the reaction tube 2 and trimethyl borate as the borate alkoxide will be described with reference to FIG.

  The quartz tube 2 is installed in the resistance heating furnace 3 and heated to a predetermined temperature. Trimethyl borate is put in the container 1 and introduced into the quartz tube 2 through the introduction tube 4 by nitrogen. On the other hand, ammonia is also introduced into the quartz tube 2 via the introduction tube 5. The introduced trimethyl borate and ammonia react in the heated quartz tube 2 to produce white powder (firing condition 1). Part of the generated white powder adheres to the quartz tube 2, but most of it is transported to the recovery container 6 by nitrogen or unreacted ammonia. A white powder (product 7) as a product is recovered from the recovery container 6.

  The temperature of the tubular furnace 3 is preferably 750 ° C. or higher. When the temperature is lower than 750 ° C., the average particle diameter of the boron nitride fine particles to be generated may be larger than 1.0 μm.

  The reaction between trimethyl borate and ammonia is completed within 30 seconds. If it exceeds 30 seconds, the average particle diameter of the boron nitride fine particles may be larger than 1.0 μm.

  As the boric acid alkoxide used in the present invention, trimethyl borate, triethyl borate, triisopropyl borate, and the like can be used. It is preferable to use it. As trimethyl borate, there is a trade name “TMB” manufactured by Tama Chemical Industry Co., Ltd. in addition to the reagents of each company.

  On the other hand, the ammonia used in the present invention is not particularly limited, but a so-called “high purity” type containing no impurities is preferable.

  Although it does not specifically limit as an inert gas, It is a gas which is hard to raise | generate a chemical reaction, For example, noble gases, such as helium, neon, and argon, nitrogen, etc. are mentioned.

  The mixing ratio of boric alkoxide and ammonia is 1 to 10 in terms of a molar ratio of ammonia / boric acid alkoxide. When the ammonia / boric acid alkoxide molar ratio is less than 1, the purity of the boron nitride fine particles may be lower than 98.0%, and when the molar ratio is higher than 10, the average particle diameter of the boron nitride fine particles is smaller than 0.01 μm. There is.

  The introduction of the boric acid alkoxide and ammonia is stopped, the power source of the tubular furnace 3 is turned off, and the white powder synthesized under the firing condition 1 is collected, and the firing is performed under the firing condition 2 using, for example, the apparatus shown in FIG.

The apparatus used under the firing condition 2 uses an alumina tube as the reaction tube 2 ′ in the resistance heating furnace 3 ′, and fills the center of the reaction tube with the white powder (product 7) synthesized under the firing condition 1, After setting in the heating furnace 3 ′, nitrogen was introduced from the introduction pipe 4 ′ and ammonia was introduced from the introduction pipe 5 ′. After raising the temperature to a predetermined temperature, baking is performed for a predetermined time. After firing, the resistance heating furnace 3 'is cooled and the fired product is recovered.
In firing condition 2, it is also possible to use an induction heating furnace.

  The temperature of the resistance heating furnace 3 is 1,000 to 1,600 ° C. Outside this range, the orientation index of boron nitride fine particles may be greater than 15.

  The reaction time of the firing condition 2 is 1 hour or more. If it is less than 1 hour, the orientation index of the boron nitride fine particles may be larger than 15, and the boron nitride fine particles may have a scale shape and low circularity.

  The atmosphere of the firing condition 2 is preferably an atmosphere of ammonia gas or a mixed gas of ammonia gas and inert gas. In the absence of ammonia gas, the boron nitride fine particles may have an orientation index greater than 15, a purity of less than 98.0%, or a scale shape with a low average circularity.

  After the reaction under the firing condition 2 is completed, the electric furnace is turned off, and the introduction of nitrogen and ammonia is stopped and cooled.

The fired product fired under firing condition 2 is placed in a boron nitride crucible and further fired under firing condition 3 in which it is fired at a predetermined temperature in a nitrogen atmosphere in an induction heating furnace.
Since the firing temperature is as high as about 2,000 ° C., it is preferable to use an induction heating furnace as the firing furnace.

  The temperature in firing condition 3 is 1,800 to 2,200 ° C. If it is lower than 1,800 ° C., the purity of the boron nitride fine particles may be lower than 98.0%, and if it is higher than 2,200 ° C., the boron nitride fine particles may be collapsed.

  The reaction time in the firing condition 3 is 0.5 hour or more. If it is less than 0.5 hour, the purity of the boron nitride fine particles may be lower than 98.0%.

  The average particle diameter of the boron nitride fine particles produced in the present invention is 0.05 to 1.0 μm. Outside this range, the dispersibility in the resin is poor and the surface smoothness cannot be obtained, and when dispersed, there is a problem that the resin layer cannot be kept high in strength.

The alignment index of boron nitride particles produced in the present invention, the ratio of the intensity I ₁₀₀ of the by powder X-ray diffraction (002) plane and intensity I ₀₀₂ of diffraction line (100) plane of the diffraction line (I ₀₀₂ / I ₁₀₀ ), and 1 to 15 from the viewpoint of obtaining high thermal conductivity.

  The boron nitride purity of the boron nitride fine particles produced in the present invention is 98.0% or more from the viewpoint of obtaining high thermal conductivity.

  The average circularity of the boron nitride fine particles produced in the present invention is 0.80 or more from the viewpoint of obtaining high thermal conductivity.

  Hereinafter, the present invention will be further described based on experimental examples.

Experimental example 1
Firing condition 1
The quartz tube 2 is placed in a resistance heating furnace 3 and heated to a predetermined temperature. Trimethyl borate was placed in the container 1 and introduced into the quartz tube 2 via the introduction tube 4 with nitrogen. On the other hand, ammonia was also introduced into the quartz tube 2 via the introduction tube 5. The introduced trimethyl borate and ammonia reacted in the heated quartz tube 2 to produce a white powder. The generated white powder (product) was recovered from the recovery container 6.

Firing condition 2
The white powder recovered under firing condition 1 was fired with the apparatus shown in FIG.
The white powder (product) collected under the firing condition 1 was filled in the center of the alumina tube 2 ′ and set in the resistance heating furnace 3 ′, and then nitrogen and ammonia were introduced from the introduction tubes 4 ′ and 5 ′, respectively. After heating up to the predetermined temperature shown in Table 1, it baked for the predetermined time, after completion | finish of baking, it cooled and collect | recovered baked products.

Firing condition 3
The fired product obtained under firing condition 2 was placed in a boron nitride crucible and fired at a predetermined temperature shown in Table 1 in an induction heating furnace in a nitrogen atmosphere. The average particle diameter, orientation index, boron nitride purity, and average circularity of the obtained boron nitride fine particles were measured. The results are shown in Table 1.
The temperature, time, and firing atmosphere of firing conditions 1, 2, and 3 are also shown in firing conditions 1, 2, and 3, respectively.
Moreover, the electron micrograph of the Example of this invention is shown in FIG. 3, and the electron micrograph of a comparative example is shown in FIG.

<Materials used>
Trimethyl borate: Reagents manufactured by Wako Pure Chemical Industries, Ltd. Trimethoxyborane ammonia: High purity type commercial product

<Measurement method>
Average particle diameter: For measurement of the average particle diameter, a laser diffraction scattering particle size distribution measuring device manufactured by Coulter, trade name “LS-230” was used.
Orientation index: measured by X-ray diffractometer (“Geiger Flex 2013” manufactured by Rigaku Corporation) in the range of 2θ = 30 ° to 25 °, and diffraction around 2θ = 27-28 ° ((002) plane) The line intensity I ₀₀₂ and the intensity I ₁₀₀ of the diffraction line near 2θ = 41 ° ((100) plane) were determined. The orientation index was calculated from the peak intensity ratio of X-ray diffraction of boron nitride, with the orientation index = I ₀₀₂ / I ₁₀₀ .
Boron nitride purity: Boron nitride purity was determined by the following method. After alkali decomposition of the sample with sodium hydroxide, ammonia was distilled by a steam distillation method and collected in a boric acid solution. The collected liquid was titrated with a sulfuric acid normal solution to determine the amount of nitrogen (N), and then boron nitride purity (BN) was calculated from the following formula.
BN (%) = N (%) × 1.772
Average circularity: After taking a particle image with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), the projected area of the particle (for example, product name “MacView” manufactured by Mountec Co., Ltd.) S) and the perimeter (L) were measured. The circularity was determined by the following formula.
Circularity = 4πS / L ²
The circularity of 100 arbitrarily selected particles was measured, and the average value thereof was taken as the average circularity of the sample.

1 Boric alkoxide container 2 Reaction tube (quartz tube)
2 'Reactor (Alumina tube)
3, 3 'tubular furnace (resistance heating furnace)
4 Boric acid alkoxide introduction tube 4 'Nitrogen introduction tube 5, 5' Ammonia gas introduction tube 6 Sample collection vessel 7 Product

Claims (2)

  Spherical boron nitride fine particles having an average particle diameter of 0.01 to 1.0 μm, an orientation index of 1 to 15, a boron nitride purity of 98.0% by mass or more, and an average circularity of 0.80 or more.   After reacting boric acid alkoxide having a molar ratio of ammonia / boric acid alkoxide of 1 to 10 with ammonia in an inert gas stream at 750 ° C. or more within 30 seconds, ammonia gas or ammonia gas and inert gas A method for producing spherical boron nitride fine particles, comprising heat treatment at 1,000 to 1,600 ° C. for 1 hour or more in a mixed gas atmosphere, and further firing at 1,800 to 2,200 ° C. for 0.5 hours or more in an inert gas atmosphere.